usually we say 你好 instead of 你好吗？ I found most of the chinese learners like saying 你好吗？ if you want to be more native,just say 你好.

有“区”别：（不是“出”别） 你好！------问候语，就像楼上所说hello 你好吗？---（1）问候，比如HOW R U? （2）或者询问对方状况，比如R U OK?

有区别哦。。

In my opinion ,你好and你好吗are different.The first means hello as a normal greeting ,expecialy the first time people meet.It is the first word when you begin your talking.你好吗means"how is everyting going?"appear between friend or known people long time no see.we Chinese don't use it as greeting !

ni hao is like 'yo!' ni hao ma is more like 'how are you doing, i really want to know' That is why i never ask 你好吗？ lol :P